Furnace for melting metals and alloys



Feb. 14, 1950 P. M. HULME FURNACE FOR MELTING METALS AND ALLOYS Filed Oct. l, 1946 |NVENTOR )jg/F1740 /ff//rlIf//r BY v QW ATTORNEYS meme rgb. 14,1956

UNITED STATES PATENT OFFICE` FURNACE FOR MELTING METALS AND ALLOYS APhilip M. Hulme, Stamford, Conn., asslgnor to Air Reduction Company, Incorporated, a corporation of New York Application October 1, 1946, Serial No. 700,557 2 claims. (ci. 26a-33) l This invention relates to furnaces for melting metals and alloys.

The principal object of the invention is to provide an improved furnace in which metals, particularly non-ferrous metals, having a melting point ranging up to about 2000 F. can be rapidly melted, and if desired, melted in a controlled atmosphere.

Another object is to provide a furnace in which the heat for melting the metal is supplied by radiant gas burners.

A further object is to provide a furnace which comprises a refractory-lined shell within which is positioned a retort and which is studded with radiant-heat-type burners at least in the region below the retort.

The accompanying drawing illustrates more or less diagrammatically a furnace embodying the invention. In the drawing:

Figure 1 is a vertical transverse section through the furnace; 4

Fig. 2 is a front elevation of one of the radiant gas burners employed to heat the furnace; and

Fig. 3 is a vertical section taken on the line 3--3 of Fig. 2.

Referring first to Fig. 1, the furnace in its preferred form comprises a substantially globular retort I provided with diametrically opposite cylindrical extensions 2 and 3 at one of its horizontal axes. The retort I is suspended in an outer substantially globular shell 4, the wall of which is spaced throughout a substantial distance away from the wall of the retort. The outer shell has a refractory lining 5 which is studded with a plurality of radiant heat-type burners 6, a group of which are at least in the region below the retort, the detailed construction of which burners will be later described.

The retort I-is preferably mounted for rotation relative to the outer shell 4 about the axis of its cylindrical extensions 2 and 3 if the retort is to be rotatable, although in some cases it maybe non-rotatable as hereinafter described. This is preferably accomplished by making the cylindrical extensions 2 and 3 long enough to project outwardly beyond the shell and providing the extensions near their outer ends with flanges 1 and 8, respectively, which may be welded or otherwise secured to the extensions. Brackets 9, attached at angularly spaced regions to that side of the shell through which the cylindrical retort extension 2 projects, vcarry rollers I 0 which rotatably support and guide the flange 1. Similar brackets II attached at angularly spaced regions to the opposite side of the shell carry flange 8.

rollers I2 which rotatably support and guide the Rotation is imparted to the retort I in any suitable way as by means of an electric motor I3 mounted on one of the brackets II and which serves to drive a gear I4, fastened to the retort extension 3, by means of a pinion I5.

The retort may be made of cast iron or refractory material, depending upon the temperature it is called upon to withstand, but when made of certain refractory materials it should be a non-rotary retort.

The entire furnace is suspended on trunnions on the outer shell the axis of which is at right angles to and in the same horizontal plane with the axis of the cylindrical retort extensions 2 and 3. One of the trunnions appears at I6. The trunnions are mounted in bearings carried by a pair of floor brackets or standards one of which appears at II. The entire furnace can be tilted about the axis of the trunnicns to pour the molten metal through the cylindrical retort extension 2 after the melting operation. Any suitable mechanism may be employed for tilting the furnace, such as a motor geared to one of the trunnions, or a motor I8 which drives a worm Il meshing with rack teeth 20 on the outer shell.

The outer ends of the cylindrical retort extensions 2 and 3 are adapted to be closed by doors 2| and 22, respectively, which may be clamped in closed position by a clamp 23 to form a gastight seal. The doors 2| and 22 are provided with i valve controlled conduits 25' and 26, respectively, by means of which a suitable gas can be run through the retort when it is desired to perform the melting operation under a controlled atmosphere.

A radiation pyrometer 21, positioned at the underside of the furnace, has a tube 28 which extends through the outer shell l and its refractory lining so that the pyrometer is directed toward the inner retort and indicates its temperature.

The construction of the radiant heat-type burners which are preferably gas burners is best shown in Figs. 2 and 3. Each burner comprises l a body portion 29 of refractory material having at one side a concave surface or cup 30. A transverse central opening 3I leads from the opposite side of the body to the central region of the concave surface. When combustible gas or other combustible fuel mixture is admitted through the opening 3|,y and distributed by a refractory plug 32, and ignited, it produces a flame system 33 which heats the concave surface 3l to a high temperature. As shown in Fig. 1 the radiant burners are all positioned so that the concave surface of each burner faces the inner retort I and radiates and directs heat toward the retort. All of the gas burners above the retort l, i. e. those above the level of the molten metal in the retort, are connected to a gas manifold 3|, and those below the retort, i. e. those below the level of the molten metal, are connected to a similar gas manifold 35. The burners above the retort are supplied with a mixture of air and a fuel-gas such as acetylene. The burners below the retort are supplied either with the same gas mixture as the upper burners or with a mixture of oxygen or oxygenated air and fuel-gas.

The furnace is operated as follows: The retort is charged with the metal or alloy to be melted through one or both of the cylindrical extensions of the retort. The doors 2| and 22 are then closed, the burners started, and the inner retort slowly rotated. If a controlled atmosphere is to be used, the retort is purged of air and the control gas is passed through the retort during the melting operation by admitting it through either conduit 25 or 2B and discharging it by means of the other conduit. The metal to be melted in contact with the inner surface of the retort will receive heat by radiation from the radiant burners to the outer surface of the retort, by conduction through the wall of the retort, and by conduction from the inner surface of the retort to the metal. At the start of the melting operation, when the metal in the retort isl still solid, some pieces of the metal will, of

course, be spaced from the inner surface of the retort and heat will be transferred through these spaces to the metal by radiation. While the hot combustion gases of the burners passing over the outer surface of the retort will transfer some heat from the burners to the retort by convection, the greater portion of heat transfer from the burners to the retort will be by radiation. For metals melting below 1600 F., theabsolute temperature of the surface of the retort should be limited to a maximum of about l800 F. which will be attained only after the metal of the charge is completely molten, but of course the absolute temperature of the retort surface will start well belowthis figure. The higher the absolute temperature of the radiant burner cups can be made right from the start, the more rapid will be the heat transfer during the melting period. To attain this high temperature the lower burners are preferably supplied with oxygen or oxygenated air, instead of air, to insure complete combustion at the concave surfaces of Rotating the retort prevents local the burners. overheating and damage to the retort by continually moving the Wall of the retort into the upper zone where the burners are operated principally to maintain soaking heat. Some heat will also be transferred through the wall of the upper portion of the retort and will be radiated down to the charge in the lower` half of the retort.

As soon as the charge is melted, -as indicated by the pyrometer; the supply of oxygen or oxygenated air to thevburners is shut offA and the burners are operated solely to maintain the metal hot until it is poured. The molten metal in the retort is represented at 36. It is poured into-the casting ladle through the cylindrical retort extension 2 whenthe furnace is tilted about the axis of its trunnions.

If the furnace is to be used for melting metals melting furnaces.

or alloys having a melting point below 1600u F.. the inner retort may be made of cast iron or one of the heat-resistant high nickel-chrome alloy irons. If the furnace is to be used for melting copper base alloys, the inner retort should be made of a more heat-resistant material such as silicon carbide. Since copper melts at around 1981 F., the retort, if made of metal, would not withstand the high temperature necessary to melt the charge. Silicon carbide will withstand temperatures far in excess of 1981 F. and has excellent heat'conductivity, but if the retort is made of this material it should be a non-rotary retort since silicon carbide is a bonded ceramic material and does not have the ystrength necessary for a rotating retort. However, it is such a good refractory that the need for rotating the retort no longer exists with this material.

An ordinary refractory can be used for the lining of the outer shell, but for the highly heated concave radiant surfaces of the radiant burners, zirconia or thoria or some other refractory capable of withstanding temperatures approaching 4000 F. should be used. The refractory material capable of withstanding this high temperature may, if desired, be in the form of a liner at the concave surface of the burners, or the entire body of the burners may be made of such refractory.

The furnace is adapted to melt aluminum in an atmosphere of nitrogen at rates far exceeding anything possible with conventional metal Magnesium can be rapidly melted in'an atmosphere of sulphur dioxide, and zinc base alloys can be melted in an atmosphere of nitrogen to give a minimum loss due to volatilization and drossing. Lead, babbitt and other metals having a melting point not exceeding 2000 F. can be rapidly melted in the same manner.

I claim:

1. In combination with a furnace for melting metals comprising a refractory lined shell, a retort within said shell spaced at all points a subl stantial distance away from the refractory lining of said shell, means for charging metal into said retort and for discharging molten metal therefrom and a plurality of radiant-heat-type fuel burners studding the refractory lining of said shell for supplying heat to said retort, each burner comprising a refractory member having a heat-radiating concave surface; the improvement in which a group of radiant-heat-type burners are at least in the region below the retort and have their concave, heat-radiating sur- -faces facingv the retort, whereby heat is radiated from said concave surfaces directly onto the underside of the retort.

2. In combination with afurnace for melting metals comprising a refractory lined, substantially globular shell, a substantially globular retort within said shell spaced at all points a substantial distance away from the refractory lining of said shell, means for charging metal into said retort and for discharging molten metal therefrom and a plurality of radiant-heat-type fuel burners studding the refractory lining of said shell for supplying heat to said retort, each burner comprising a refractory member having a heat-radiating concave surface; the improvement in which some of the radiant-type burners are above the retort and some below the retort and have their concave heat-radiating surfaces facing the retort, means -for supplying a combustible fuel inixture to the burners above there- 5 tort, and separate means for supplying a combustible fuel mixture to the burners below the retort, whereby the radiant burners below the retort may be operated at a temperature higher than that of the burners above the retort.

PHILIP M. HULME.

REFERENCES CI'IIED The following references are of record in the le of this patent:

Number UNITED STATES PATENTS Name -Date Maohlet June 2, 1931 Hess Sept. 17, 1940 Hess Sept. 17, 1940 Hess Sept. 17, 1940 Hulme et a1 Dec. 9, 1941 Bonsack Oct. 19, 1943 

